#app {
    color: red;
    display: flex;
    backface-visibility: hidden;
}
#box1{
    width: 100px;
    height: 100px;
    background-image: url(../img/1.jpg);
    background-repeat: no-repeat;
    background-size: 100% 100%;
}
#box2{
    width: 200px;
    height: 200px;
    background-image: url(../img/2.png);
    background-repeat: no-repeat;
    background-size: 100% 100%;
}
#box3{
    width: 300px;
    height: 300px;
    background-image: url(../img/3.jpg);
    background-repeat: no-repeat;
    background-size: 100% 100%;
}
span{
    color: #FFF;
}